Commissioner Edward F. Davis, whose seven-year tenure leading the Boston Police Department has been marked by falling violent crime rates and seared by the Marathon bombings in April, will announce Monday that he is resigning, and he will pursue a fellowship at Harvard University, according to a person with knowledge of his plans.

Davis will leave his post in the next 30 to 60 days, his spokeswoman said, just as Mayor Thomas M. Menino’s tenure is ending. The departure comes as some mayoral candidates have faulted Davis for what they see as his insufficient effort to diversify the police department.

In a statement, Menino thanked Davis for his “tremendous work over the past seven years,” and said he would work with Davis to appoint an interim police commissioner until a new mayor picks a permanent replacement.

To many in the city, the announcement was not a surprise. There had been speculation that Davis would seek a more high-profile job following the Marathon bombings, after his calm and reassuring response garnered him national praise. He also oversaw a 30 percent decrease in violent crime over his nearly seven years as commissioner, though at times there were spikes in the numbers of murders and shootings.

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A person close to Davis said the commissioner will explore other career options while he is at Harvard. The fellowship is with the Institute of Politics, where Davis will teach and take courses, said an official with direct knowledge of Davis’s plans.

Being at Harvard will give Davis time to consider his next steps, time he would not have while running a department of 2,141 officers.

“The job is so extremely busy that it’s very difficult to explore other opportunities,” the person close to Davis said.

The person asked for anonymity because the commissioner had not formally announced his departure. Davis had been thinking of leaving for months, the person said.

“He views himself as a team with the mayor,” the person said. “In the past couple of weeks he just felt like it was time.”

The official said that Davis wanted to make the announcement before the preliminary election on Tuesday, when voters will whittle down the field of mayoral candidates from 12 to two, who will face off in a general election on Nov. 5.

Davis wanted to avoid any speculation that his decision to leave was influenced by the outcome of the election.

“The new mayor should have a clean slate and pick the commissioner he or she wants,” said the official.

Davis’s spokeswoman, Cheryl Fiandaca, said Davis handed his resignation letter to Menino on Saturday and will discuss his future plans at a news conference at police headquarters Monday morning. Davis declined to speak to a reporter who went to his Hyde Park home.

Since Menino announced he would not seek reelection in March, department and community leaders had speculated on whether Davis would leave with the mayor, who will step down on Jan. 6.

It was a turnabout since April, when Davis, 57, was praised for his leadership in the aftermath of the bombing at the finish line of the Boston Marathon, an attack that killed three people and injured more than 260 others. In May, Davis received honorary degrees from Suffolk and Northeastern universities and spoke at the University of Massachusetts Lowell commencement.

Throughout his tenure, many community leaders in neighborhoods most affected by gun violence lauded him for his accessibility and his emphasis on community policing, a strategy that calls on police officers to build relationships in the neighborhoods they patrol.

But many in the department resented the way he disciplined officers, accusing him of unfairly punishing those who were unpopular with the administration and insulating officers that he and Menino favored. Davis, who took over the department when it was reeling from a steroid abuse scandal, has said the disciplinary system was fair and each case was handled on individual merits.

Davis also was never able to appease leaders of the Massachusetts Association of Minority Law Enforcement Officials, who accused the commissioner of failing to promote qualified officers of color to high-ranking positions.

The organization held a no-confidence vote against Davis in August and the group’s criticism soon infiltrated the mayoral race, with the minority law enforcement group vowing to oppose any candidate who said they would keep Davis as commissioner.

Over the past several weeks, many candidates agreed with the group that Davis needed to do more to diversify the top ranks of the department. In recent days, one mayoral candidate, John Barros, who initially supported keeping Davis, said that if elected he could not commit to keeping him as commissioner.

On Sunday, Barros said in a statement that the city should honor Davis “for the exemplary leadership he demonstrated in one of Boston’s darkest moments after the Marathon bombings.”

“We need to ensure that the next commissioner has the qualifications and experience to lead the Boston Police Department into its next chapter, with a particular focus on building a department that reflects Boston’s diversity, while increasing community-based policing,” Barros said.

“We need to get more African-American, Latino, and Asian candidates interested in police work and Ed has tried very hard to do that,” Conley said during a campaign stop in West Roxbury Sunday. “He has recruited heavily. I know his heart’s in the right place. He always wanted the Police Department to reflect the diversity of Boston and he was striving towards that goal.”

Conley said he was disappointed that Davis would be leaving, a sentiment shared by many community leaders who worked closely with him over the years.

“I will miss him,” said Emmett Folgert, executive director of the Dorchester Youth Collaborative in Fields Corner. “He was responsive to community organizations. He was very frank. . . . I think he was a very forthright person.”

Jorge Martinez, executive director of Project R.I.G.H.T., a Grove Hall-based nonprofit that works to stem violence, said Davis had been a solid leader. “He was transparent as someone can be in his position,” Martinez said. “He’s grappled with some of the most horrific things that can happen to a person in his position and he’s handled that admirably. He’s done good.”

Larry Ellison, a Boston police detective and president of the minority law enforcement group, said his organization will continue to oppose any candidate who expressed support for keeping Davis.

“His resigning doesn’t resolve the fact that they were willing to keep on someone with that kind of horrible track record on diversity,” Ellison said.

Michael Curry, president of the Boston chapter of the NAACP, said Davis’s leadership in the aftermath of the Boston Marathon bombings was “masterful,” but said he leaves his post without having adequately addressed the issue of diversity or the high rate of unsolved murders in predominantly black and Latino neighborhoods.

“All of our stories are complicated,” Curry said. “In his case, I think people will look back at the many successes he had as police commissioner as well as the many missed opportunities.”

Davis had clearly become frustrated by MAMLEO’s criticism in recent weeks. In an open letter posted on the department’s website, he noted that 42 percent of his command staff – who are appointed by the commissioner — are black, Latino, or Asian, and he called the group divisive.

Charlotte Golar Richie, another mayoral candidate and the only woman running for the position, said that if she is elected she would consider hiring a minority or woman to replace Davis.

“I know that there are strong capable women in the department who would be worthy of consideration,” she said. “I will say that we will consider a wide range of folks who would be capable and interested in stepping into that role. We’ll look at city government in ways that we’re going to ensure that city government as a whole reflects the diversity of our city.”

Maria Cramer can be reached at mcramer@globe.com. Follow her on Twitter @GlobeMCramer. Globe staff writer Wesley Lowerly and Joshua Miller and Globe correspondent Matt Rocheleau contributed to this report.

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